Dopamine D1-D5 receptor protein immunohistochemistry in dog pial arteries

The localization of dopamine D1-D5 receptor protein was investigated in different sized dog pial arteries. This was done to further understand the pathophysiology of cerebrovascular dopaminergic system in migraine. The study was performed in sections of dog brain including the pia-arachnoid membrane, which were processed for indirect immunohistochemistry using antibodies raised against dopamine D1-D5 receptor protein. A faint dopamine D1 receptor protein immunoreactivity was observed in smooth muscle of the tunica media of different sized pial arteries. Dopamine D2 receptor protein immunoreactivity was located in the adventitia and adventitia-media border of pial arteries. In the same area tyrosine hydroxylase immunoreactive nerve fibers were found. No dopamine D3 receptor immunoreactivity was detectable in dog pial arteries. A faint dopamine D4 receptor protein immunoreactivity was observed in dog pial arteries, with a localization similar to that of D2 receptor protein. A moderate dopamine D5 receptor protein immunostaining was observed in smooth muscle of the tunica media. These findings indicate that dog pial arteries express dopamine D1-like (D1 and D5) and D2-like (D2 and D4) receptor subtypes and display, respectively, a muscular (post-junctional) and probably prejunctional localization. These results, the first analysis of dopamine D1-D5 receptor subtype distribution in the cerebrovascular tree, suggest that dopamine is involved in the regulation of cerebral circulation. These finding may help evaluate the role of cerebrovascular dopaminergic mechanisms in the pathogenesis of migraine.